The deposition of material upon a substrate by the use of an electric arc is well known. FIG. 1 depicts a typical deposition apparatus 10. The process takes place in a vacuum chamber 12 which encloses a substrate 14 which is to be coated and an electric arc electrode assembly 16, having an anode 18 and a cathode 20. Material 24 to be deposited is placed in a receptacle 26 formed in the cathode 20 of the electric arc electrode assembly 16. The substrate 14 to be coated is placed near the electric arc electrode assembly 16. A potential is applied between the anode 18 and the cathode 20 of the electric arc electrode assembly 16 which are physically in contact and current flows between them, once the arc is ignited. As current flows between the cathode 20 and the anode 18, the material 24 to be deposited is vaporized and ionized forming a plasma 30 which maintains current flow even as the anode 18 and the cathode 20 are physically separated. The ions of the plasma 30 interact with the surface of the substrate 14 to be coated and are deposited thereupon. It should be noted, in the case where the cathode 20 is constructed from the material 24 to deposited, the cathode 20 need not contain a receptacle 24 and instead the cathode 20 itself is consumed in the deposition process. This form of deposition, in which material is deposited from the cathode region, may be termed cathodic vacuum arc deposition.
Alternatively, the anode 18 of the electric arc electrode assembly 16 may be used as the source of the material to be deposited. In such a case, where the material is deposited from the anode region, the deposition is referred to as anodic vacuum arc deposition.
In anodic vacuum arc deposition, an electric arc 30, which forms between the anode 18 and the cathode 20, is initiated by either electrical means or by physical contact between the anode 18 and cathode 20. Once the electric arc 30 forms or ignites, the anode 18 and the cathode 20 are separated and the arc is maintained by the material ionized from the anodic region during initiation. An example of anodic arc deposition may be seen in application Ser. No. 07/934,925, now U.S. Pat. No. 5,302,271, the whole of which is incorporated by reference herein. In conventional vacuum arc deposition systems, the quality and character of the material being deposited is highly variable. Anodic arcs produce mainly fine, neutral particles with only about 20% of the particles being ionized. Deposition of these fine neutral particles onto a substrate results in production of an excellent film having very fine granularity and a high optical quality. However, the molecular structure of the deposited material may not be adjusted to fit the needs of a particular application, such as for the production of diamond and carbon nitride coatings. The particles produced by an anodic arc do not have sufficient energy to affect the bond or crystalline structure of the deposited material.
Cathodic vacuum arcs, on the other hand, produce a much larger population of ionized particles (approximately 400% more) compared to anodic arcs. The particles produced by a cathodic vacuum arc include large macroparticles of material, neutral particles, and a population of ionized particles with different energy levels. Deposition of these particles results in a coarse coating of material forming on the substrate, due mainly to large fraction of larger macroparticles. Due to the macroparticles, the resulting coating of coarse material is not of optical grade as produced in an anodic arc. However, the larger fraction of ionized particles generated by a cathodic arc allows the substrate to be exposed to particles that, once accelerated to sufficient velocities, are capable of transmitting enough energy, through mechanical collisions, for altering the molecular structure of the film.
During cathodic arc deposition, the impinging ionized particles transfer their energy to the substrate film. The energy received from the impinging ions produces a variety of enhanced crystalline and bond structures within the deposited material, depending on the energy level of the impinging ionized particles. The resulting films produced by a cathodic arc possess a molecular structure that is harder and denser than those generated by an anodic arc. However, there is presently no method to select ions with a specific energy level from the population of ionized particles generated by the cathodic arc.
Hard carbon films with diamond-like bonding (Diamond-Like-Carbon, (DLC) films) are used as protective overcoats in many industrial applications such as a magnetic computer hard disk. DLC films also have a higher thermal conductivity than bulk diamond and have an excellent potential to provide an efficient heat sink. The most challenging problems in the coating of DLC films are the high stress in coated films and the adhesion of the films to the substrate. CN.sub.x films exhibit improved adhesion and a reduction in the interfacial tension between the films and substrate. Other processes, such as sputtering, produce CN.sub.x films. However, such films do not possess enhanced hardness or adhesion that are required in computer hard disk applications, jet turbines, heat sinks, etc.